SOME FACTORS INFLUENCING YIELD TRENDS OF SUGARCANE IN PAPUA-NEW-GUINEA

Commercial rainfed sugarcane cultivation in Papua New Guinea was begun in the early 1980s by Ramu Sugar Ltd. Over the last 15 years, annual cane yields have ranged from 28 to 88 tonnes/hectare, this wide variat ion being largely explained by sudden and catastrophic infestation by moth stem borers, cicadas, white grub and Ramu stunt virus. To a lesse r extent yields were affected by weed competition. Changes in soil pro perties under continuous cultivation included decreases in pH, availab le phosphorus and exchangeable potassium, and some preliminary data su ggest soil compaction. Leaf nutrient concentrations of nitrogen, phosp horus and potassium also declined slightly. It is concluded that yield s were largely influenced by insect pests and diseases, but that the m anagement of soil fertility is likely to become increasingly important once those problems have been solved.